This invention is in the field of sewing machines, more particularly, it is concerned with a twin needle memory device for an electronically controlled sewing machine having an operator interface through proximity switch devices.
Increasingly, modern day appliances are making use of touch control panels which use touch activated switch means to detect the presence of an operator's finger selecting a capability or condition. This approach is particularly well suited to an electronically controlled sewing machine because of the multiplicity of capabilities and conditions from which a selection may be made simply by the touch of an operator's finger.
However, in the field of zig zag sewing machines, there exists a condition which may be a hazard to an operator if not retained to survive a power shut off. The condition referred to is the twin needle mode of operation wherein, for example, a particularly decorative stitch capability may be effected using two needles with different colored threads. In normal single needle operation, the sewing machine may be capable of, for example, a bight, or lateral movement of the sewing needle, of approximately 6 millimeters. In the twin needle condition or mode of operation, however, two sewing needles are used spaced apart approximately 21/2 millimeters. It is apparent that neither needle may undergo 6 millimeter lateral motion without causing the other needle to harpoon the throat plate outside of the normal aperture required to permit passage of the needle to a rotating looptaker beneath the throat plate. If an attempt is made to enlarge the aperture through which the sewing needles extend, the capacity of the rotating looptaker to catch a loop of thread from the sewing needles may be exceeded. Therefore, the only logical choice is to provide means, effective upon the initiation of the twin needle condition, to limit the permissible lateral motion of the sewing needles. In heretofore known electronically controlled sewing machines, this has been accomplished by utilizing a mechanical switch which, in the twin needle position, reduced the amplitude of the signal in proportion to the reduction in swing amplitude, or bight, required for the situation wherein multiple needles are used. The mechanical switch thus utilized remains in the selected position until deliberately moved by an operator in the course of stitching operation on a garment. However, it is apparent that the use of a touch control panel utilizing a plurality of proximity or momentary contact switches and the use of a single mechanical switch to maintain a twin needle condition are not esthetically and functionally compatible.
What is required is a means of attaining a twin needle condition through the use of touch activated switch means, which twin needle status is retained until deliberately changed by an operator. In the event of a power down condition, it is necessary that, upon reinitiation of power, the pre-existing status of twin needle condition be reinstated in order to prevent the possible hazard to an operator and damage resulting from resumption of a full bight condition with a twin needle inserted in the sewing machine.